whoa, whoa, whoa.....FULL STOP....
481 is a museum piece with only 467 miles. highly doubt it will become a driven Buick. don't mess with the chip. that is not your problem.
I hope the TPS voltage values were a typo...set the TPS to .42V to .44V with key ON, engine OFF. verify while sitting in driver seat that WOT TPS voltage is about 4.4 to 4.6V. actually, I believe anything above 4.0V, the ECM enters POWER ENRICHMENT mode.
start car and let warm up to operating temp about 160F. now in CLOSED LOOP. verify IAC counts to be between 10 and 30 and not bottomed out at 0. adjust IAC via spring locked screw on throttle body - it's under the silver colored vinyl cap - driver's side. when adjusting IAC, have to go back and double check TPS because the adjusting screw to set IAC moves the throttle plate thus changing TPS value. Where you noted setting TPS to .47, is high. At about .48V signal, the ECM thinks the car is driving. so get the TPS back to .42 to .44 as a start.
with engine running at idle in CLOSED LOOP verify the MAF is reading airflow....should be about 8 at idle of 775 RPM. verify the flow rate value increases with increase in engine RPM.
since this is a concours example, I'm more believing that old gas is a problem like Rick (X ray) noted. so fresh gas would be great. a new fuel filter is suggested.
if the tank is full, locate the fuel pump prime wire connector, black which is taped with a green connector single wire to the A/C line at the pressure switch behind the compressor. The green connector is for an external tachometer hookup with GM's tools. using alligator clip jumper wire, the fuel pump can be operated by making the connection at the rear of the alternator and the black connector. remove the fuel rail cap and remove the schrader valve on a depressurized system. attach a hose and jump out the fuel pump to fill some cans to drain the tank.
additionally, even if fuel stabilizer was used, I'll bet the factory pintle style injectors are fouled from sitting. the image below shows how brand new stock Bosch injectors flow after only going a few hundred miles over a few years.
after cleaning, the did all flow much better, but were less than the calibration injector on the LEFT - but within tolerance.
so, injector cleaning maybe something for a to do list, but TPS, fuel filter and fresh gas should be done first.
X ray covered the "cut" wire at the oil pressure sending unit. he would know, he worked on all 547 of them.
as far as scan tools go, I use the Auto Xray 5000 and 6000 models. it has been discontinued for a bunch of years but can be found on ebay and the like. I believe Actron bought the Auto Xray product line and immediately discontinued it to eliminate the competition. the updated product available today is the Bosch-Actron CP9690 LINK to product at JEGS =>
Bosch-Actron CP9690: Elite AutoScanner Code Scanner Kit OBD-I, OBD-II and CAN | JEGS
it's the same price as a ScanMaster and gives more info and can record data and show freeze frame data for all the parameters pulled from the ECM. covers all the ODB-1 manufacturers (GM, FORD, Chrysler, Toyota) and ODB-2 and CAN. I'm not a fan of the Buick only ScanMaster - don't want anything mounted around the dash that didn't come that way from the factory.
if you're gonna take the plastic of the seats and steering wheel and pile on the miles taking a concours car to driver, then consider a TurboTweak chip. HOWEVER, I highly doubt someone would do that to an investment grade vehicle.
attached is a spreadsheet I made for the GN with a factory PROM chip. the available parameters would be the same on a GNX, although the PROM id checksum will not be a value of 144 on a GNX. it's an easy way to record values as you work thru the matter at hand.
as I've been typing for a bit now, there may be more comments since X ray's response.
